Abstract
We present an updated model of the cosmic ionizing background from the UV to the X-rays. Relative to our previous model, the new model provides a better match to a large number of up-to-date empirical constraints, including: (1) new galaxy and AGN luminosity functions; (2) stellar spectra including binary stars; (3) obscured and unobscured AGN; (4) a measurement of the non-ionizing UV background; (5) measurements of the intergalactic H I and He II photoionization rates at z ∼ 0−6; (6) the local X-ray background; and (7) improved measurements of the intergalactic opacity. In this model, AGN dominate the H I ionizing background at z ≾ 3 and star-forming galaxies dominate it at higher redshifts. Combined with the steeply declining AGN luminosity function beyond z ∼ 2, the slow evolution of the H I ionization rate inferred from the high-redshift HI Ly α forest requires an escape fraction from star-forming galaxies that increases with redshift (a population-averaged escape fraction of ≈ 1 per cent suffices to ionize the intergalactic medium at z = 3 when including the contribution from AGN). We provide effective photoionization and photoheating rates calibrated to match the Planck 2018 reionization optical depth and recent constraints from the He II Ly α forest in hydrodynamic simulations.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 1614-1632 |
| Number of pages | 19 |
| Journal | Monthly Notices of the Royal Astronomical Society |
| Volume | 493 |
| Issue number | 2 |
| DOIs | |
| State | Published - 2021 |
Funding
improved the paper. This work was supported by NSF through grants AST-1517491, AST-1715216, and CAREER award AST-1652522; by NASA through grants NNX15AB22G and 17-ATP17-0067; by STScI through grants HST-GO-14681.011, HST-GO-14268.022-A, and HST-AR-14293.001-A; and by a Cottrell Scholar Award from the Research Corporation for Science Advancement. We acknowledge Jos? O?orbe, Jonathan Stern, and Luke Zoltan Kelley for useful discussions and comments. We thank Andrew Wetzel, Nick Frontiere, and JD Emberson for testing our new model UVB in hydrodynamic simulations. We are grateful to Rychard Bouwens for providing galaxy luminosity function measurements ahead of publication, and to Jacob Shen for providing updated AGN luminosity function and spectral models also before publication. Detailed comments by an anonymous referee substantially improved the paper. This work was supported by NSF through grants AST-1517491, AST-1715216, and CAREER award AST-1652522; by NASA through grants NNX15AB22G and 17-ATP17-0067; by STScI through grants HST-GO-14681.011, HST-GO-14268.022-A, and HST-AR-14293.001-A; and by a Cottrell Scholar Award from the Research Corporation for Science Advancement.
Keywords
- Cosmology: theory
- Diffuse radiation
- Galaxies: active
- Galaxies: formation
- Intergalactic medium
ASJC Scopus subject areas
- Astronomy and Astrophysics
- Space and Planetary Science